Mechanical evidence of the impossibility of directed motion of Trypanosoma cruzi towards preferred organs in the human body, a simulation 2D model within a laminar flow.

The movement of the T. cruzi within the human blood is not completely understood. Video microscopy observations confirm forward motility of the protozoa and relate it to the deformation of the body, nonetheless there are open questions regarding the deformation of the protozoan with its motion in blood, for which a computational model would be very helpful. In this paper we introduce a computational 2D model coupled with Dissipative Particle Dynamics (DPD) to assess the mechanical feasibility of directed motion and tropism by quantify the energetic cost and hydrodynamic constraints of the parasite's motility within a laminar flow. We represented the infective trypomastigote stage of the parasite as a deformable elastic body using a network of harmonic springs with shape transitions driven by discrete geometries extracted from experimental video recordings. The structure interacts with a laminar fluid implemented via the DPD method. Coupling these models allowed us to assess the interplay between the parasite's undulatory deformation and the hydrodynamic drag forces across a range of physiological Reynolds numbers. Our model confirms that, while the parasite can self-propel in a stationary fluid, the mechanical energy required to maintain its motility kinematics increases significantly with the Reynolds number. The simulations demonstrate that hydrodynamic drag forces dominate over the parasite's thrust, making directed motion against physiological blood flow mechanically inefficient. We provide mechanical evidence that even within a conservative 2D approximation, the energetic cost for T. cruzi trypomastigotes to maintain their undulatory kinematics increases significantly under flow conditions. This suggests that long-range transport within the host is primarily driven by blood flow advection rather than autonomous motility, providing a biophysical basis for understanding the dissemination of the parasite during the acute phase of infection.